Grandmother Is Being Manipulated Into Giving Money

Long story short someone in my family is manipulating my grandmother into giving them money, i stay with my grandmother and look after her just me and her and they come and do a little bit of work around the house like mow the lawns for 30-40mins and then take $600-$800 off her everytime. They only come on her pension days as my grandma gets a decent amount of money from her late husband being in the army. The family member that is doing this to my grandma is now aware that basically the entire rest of the family don’t want her here and she isn’t respecting any of our wishes as my nan is happy to pay her basically her whole pension. Most of us have tried to talk to my grandma but she wont listen to any of us and basically is angry that we are not happy with how this family member is using her. My nan also isnt at 100% mentally with her dementia so she is easily manipulated. So far we are going through elders abuse and we are also taking her to the doctors in a few days to see if we can get a notice to say shes not 100% so i can become her power of attorney and tresspass the family members using her without my grandmas approval. Theres a little more to the story but thats basically in a nutshell. Barely any of us know who this family member is as she has only popped up in the last couple years. Any advice is greatly appreciated. TIA